Nic you've gotten some good advice here. I would agree that the bare bones cheapest method is a dremel with engraving bit or a battery.
Michael's design is tried and true, he helped with some of my questions when searching for something myself.
If you don't want to build one and have a little cash here is what I did. I bought this AC/DC variable voltage powersupply used on Amazon for $55. It didn't work but I replaced a fuse and it lit right up.
http://www.amazon.com/Elenco-XP-625...&keywords=ac+dc+power+supply+variable+voltage
It does 5 Amps so I also hope to use it as an entry level anodizer some day.
For my etching pad I found a post by Brian Fellhoelter on a different forum that is worth mentioning. He recommended cheap graphite motor brushes and real electro etching solution. I think I paid $6 for six of them on amazon. I covered the graphite with felt, which I also bought on amazon.
http://www.amazon.com/Electric-Moto...pebp=1435718242601&perid=1MNKGAZNB52D12295DN2
I had my stencils made by Patricia at IMG, who I cannot recommend enough. I also picked up her knifemakers etching solution kit which I think is a bargain if you're not sure what type you need or will be working with a lot of different steel.
My etcher is a little atypical but it works like champ thanks to the help from the community!